1. Field of the Invention
The present invention relates to disc brakes and more particularly to improvements in large area contact disc brakes for larger vehicles such as trucks, tractor-trailer vehicles in addition to other large wheeled vehicles and aircrafts.
2. Description of the Prior Art
The improvements contemplated herein relate especially to a pneumatic disc brake as described in U.S. Pat. No. 4,102,438 issued Jul. 25, 1978, and U.S. Pat. No. 5,205,380, issued Apr. 27, 1993 herein incorporated by reference.
It is recognized that a major problem with large contact-area annular disc brakes of the type described in the above patents is heat. Great strides in improving heat dissipation were achieved with the introduction of vaned discs as described in U.S. Pat. No. 4,102,438. However, vented discs of the type described required a thicker disc to retain the same strength. A thicker disc increases the axial dimension required to house the disc or discs which is at a premium in an in-wheel, concentric brake system of the type described in U.S. Pat. No. 5,205,380. It was found for instance that it was not possible to house more than one cast-iron vented disc in such a housing, thus reducing the flexibility of design of such brakes, especially where multiple discs might be an advantage.
Another problem which has had a serious social impact is brake failure due to wear. Presently, there is no known reliable brake wear gauge for determining the remaining life of a particular set of brakes linings on a truck vehicle. It is necessary to remove housing parts on the wheel in order to examine and measure the remaining thickness of the lining and the brake disc. Since such examination adds to the down time of the truck or tractor-trailer, the tendency of the operator or driver-operator is to delay such inspection, with sometimes disastrous results, often costing innocent lives in highway accidents due to failed brakes of such large vehicles.